Tag Archives: biodiversity

Did You Say Mangroves?

Dr. Randall Hughes FSU Coastal & Marine Lab

Ed Proffitt and Randall Hughes by a black mangrove

Ed Proffitt with Randall Hughes. If global climate trends continue, mangroves may start to overtake the salt marsh ecosystem along the Gulf coast. What will these new habitats look like?

IGOR chip- biodiversity 150A few weeks ago, Dr. Ed Proffitt from Florida Atlantic University visited FSUCML to give a seminar here and on campus. Ed and I have collaborated on several proposals, so we used the visit as an opportunity to get out in the field and toss around some new ideas.

Ed has done some really interesting work on the interactions between mangroves and salt marsh plants in Tampa Bay and the Indian River Lagoon, and he wanted to see some mangroves in this area. I recalled having seen a few young red mangroves last year at some of our sites, but none of them survived this past winter (which is why we generally don’t find them around here – they can’t withstand the cold temperatures that we get every few years). However, black mangroves do extend into this portion of the Gulf, and I knew of a place where we may find one or two small ones to look at.

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Black mangrove (Avicennia) growing in St. Joe Bay

To my surprise, we found a lot more than one or two! And although they are small (think small shrub, rather than tree), some of them, such as the one shown here, had aerial roots extending out 14-15m, suggesting that they have been around at least 5-10 years (by our best guess).

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Avicennia flower. These mangroves are insect-pollinated, and we saw lots of bees buzzing around.

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Avicennia propagules growing on the maternal tree.

Also, most of the larger ones had both flowers and propagules (seedlings that are retained on the tree) on them.

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Avicennia propagule that has dropped to the ground and started to take root.

As we looked around, we noticed more and more small mangroves in the marsh – probably the seedlings from some of the nearby larger trees – and we even found some of this year’s propagules that were starting to root in the sediment.

As I mentioned, black mangroves are known to grow in the Panhandle and west into Louisiana and Texas, so it really isn’t that surprising that we found them in St. Joe Bay. What is surprising, at least to me, is that they are as abundant as they are in a site where I previously thought there were only a few. Where else may they be in the bay? And are they increasing in abundance each year? What impact do they have on the marsh plants and animals? The questions abound. With our curiosity and Ed’s insight and experience, we are now starting to pursue the answers.

Randall’s research is funded by the National Science Foundation.
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The search for patterns

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip- biodiversity 150The end of summer is a good time to pause and think about any general patterns that emerge from observations over the course of the last year(s). Sometimes it is easy to get swept up in the minutiae of individual projects and forget about the big picture. Of course, these patterns aren’t definitive (i.e., don’t quote me on this!), but they can be useful to think about, particularly when considering future avenues of research.

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Marsh island in St. Joe Bay viewed from the waterand marshes on the edge of the mainland.

So what sort of patterns can I describe to you after two summers in the marshes of St. Joe Bay? One that doesn’t take a PhD to recognize is that there are two distinct types of marshes that we sample: marsh islands and marshes on the edge of the mainland.

But aside from the obvious fact that one is an island and the other is not, there are some additional interesting differences:

1. The slope of marsh islands is typically greater than mainland marshes, so that you move quickly from plants that can tolerate frequent flooding (cordgrass) to plants that are more “terrestrial” (pickleweed, saltwort, etc.). On islands this transition can occur within a few steps of the water’s edge, whereas mainland marshes typically have a large area (I like to think of it as a football field) dominated by cordgrass.

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Elevation on islands changes rapidly compared to the mainland. Even slight differences in height can influence plant communities.

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Sampling a mainland marsh in St. Joe Bay.

2. Marsh islands tend to have fewer periwinkle snails than mainland sites, although they are certainly present.

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Abundant snails in a mainland marsh.

My guess is that the snail predators (blue crabs, crown conchs) that lurk just at the water’s edge have greater access to snails on the islands at high tide, because they can move in from all sides of the island. In contrast, the predators near mainland sites have only one point of entry into the marsh.

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Blue crab lurking in the seagrass at the edge of the marsh during low tide.

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Crown conch foraging for snails in a lab experiment.

3. Perhaps not surprisingly given that they are surrounded by water, the marsh islands typically have fewer grasshoppers jumping around. We’ve also had far fewer snake encounters on islands, which I consider a good thing. Probably because land-based predators such as snakes, raccoons, etc., are less frequent on islands, we also observe greater numbers of nesting birds on the islands than at mainland sites.

4. One clear difference that I can’t explain but hope to examine in the future is that cordgrass plants collected from the islands (which can only be done with a special permit from the Department of Environmental Protection) survive better in our greenhouse at the lab than those from mainlands. It may simply be the growing conditions, or island plants may be hardier overall. Stay tuned.

As we continue to process, enter, and analyze data, there should be additional trends emerging. And we’ll likely find out that some of the patterns we think we see don’t hold up to the test of actual data. And so goes the process of science!

Randall’s research is funded by the National Science Foundation.
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Autumn in the marsh

Dr. Randall Hughes FSU Coastal & Marine Lab

Marsh periwinkles climbing on a cordgrass reproductive stem

A cordgrass reproductive stem stands above the surrounding plants.

IGOR chip- biodiversity 150 One doesn’t need to look at a calendar to realize that fall is upon us – recent cool mornings are a welcome sign. The marsh is also showing signs of change, with cordgrass flowering shoots springing up everywhere.

These stems are quite noticeable – they are taller than non-reproductive plants, and they have a “feathery” appearance due to the reproductive structures at the tops of the stems.

As I’ve mentioned before, cordgrass is one of those plants (like strawberries) that can spread by underground rhizomes, putting up new stems along the way. Alternatively, it can reproduce the “traditional” way, with reproductive stems that broadcast and receive pollen via the wind, ultimately producing seeds that fall to the sediment, get buried, and then germinate to produce new seedlings. Though conventional wisdom is that most new cordgrass stems are produced vegetatively by spreading rhizomes, it’s clear at our sites that these plants are investing a lot of energy in the other form of reproduction! Continue reading

Is it over?

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip- biodiversity 150Since my last post, oil has stopped spewing from the Deepwater Horizon well, a very welcome development in what has been a long and grim story. Although it is tempting to feel that we are out of the woods, all one needs to do is consider the amount of oil that has entered the Gulf to realize that it will be a long time before we fully understand the ecological impacts of this disaster, much less fully recover from it.

That said, the probability that the marshes I study in St. Joseph Bay and Apalachee Bay are going to be directly impacted by oil has declined dramatically. You may wonder, were our efforts to collect “pre-oil” data wasted? The answer is no, for a number of reasons:

Continue reading

Eating contest: grasshoppers vs. snails

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip- biodiversity 150One of the really interesting aspects of the marsh community is that it is a mix of sea-based and land-based critters. At low tide, insects and rodents move in, whereas at high tide, snails, fish, and crabs dominate. The 2 most common plant grazers at our sites illustrate this dichotomy :

one is a land-based grasshopper(Dicromorpha elegans),

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and the other is a sea-based snail (Littoraria irrorata).

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In addition to being very abundant in our sites, the grasshoppers and snails leave distinctive grazing marks that alert us to their activity. Grasshoppers tend to chew large pieces out of the margin of the leaves, often resulting in the removal of large portions of the upper leaves. Snails, on the other hand, create razor-blade like incisions in the middle of the leaf:

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spartina with grasshopper grazing damage

Snail grazing scar

periwinkle grazing scars on spartina

We are interested in the potential for interactions between these 2 consumers, because they occur together in abundance at several of our sites. A preliminary experiment last summer suggested that snails somehow deter grasshopper feeding, even though neither animal can directly harm the other. (In fact, as you can see from the video, sometimes the grasshoppers even hang out on the snails’ backs!) However, it is possible that snails leave a “slime” trail that the grasshoppers don’t like, or perhaps snail grazing causes the plants to produce chemicals that make it less likely that grasshoppers will eat them.

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To find out more, we are repeating the same experiment (with some minor modifications) to look more closely at how much snails and grasshoppers eat when they are alone versus how much they eat when they are together. Because it is difficult to make grasshoppers stay where you want them, we are doing the experiment in mesh cages inside “mesocosms” (science-speak for large buckets) at the FSU Coastal and Marine Lab.

The mesocosms are set up to mimic the natural tidal cycle, with both high and low tides on a regular basis. We measured the height and number of stems of all the plants in each mesocosm at the start of the experiment, and we’ll take these same data at the end of a couple of weeks to see which species has the largest effect, and whether their combined effects are different from what we expect based on what they eat alone.

As an aside, this experiment is a good example of one of my ecologist’s rules of thumb: you can never do an experiment just once. There are certainly exceptions to this rule. (For example, when you have lots of experience with the animals you are experimenting with, when the experiment is just too large to repeat, or when the experiment relies on something you can’t manipulate, such as an oil spill.) However, I find that it generally takes one go-around to work out the kinks, figure out the relevant time frame, and discover unanticipated results. Then I can be much more confident the second time around that the patterns I am seeing are real!

The music in the piece was by Ric Edmiston.  We are always looking for local musicians to score our videos.  If you are interested and already have some music recorded, we would love your submission.

Randall’s research is funded by the National Science Foundation.

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Can plant species diversity provide protection against oil?

Dr. Randall Hughes FSU Coastal & Marine Lab

Watch Dr. Hughes’ species diversity experiment.  The results could help determine how best to restore marshes affected by oil.

IGOR chip- biodiversity 150With oil arriving on FL beaches, the race is on. We’ll be out in our sites this week collecting more data. We want to be sure that we know as much as possible about:

(1) the condition of our sites before oil arrives;

(2) the amount and specific location of any oil that does reach our sites; and

(3) the response of the marsh plants and animals to this oil.

We expect that there will be considerable variability in the degree and extent of damage to our sites, both because oil exposure will likely be patchy (at least at first), and because marshes are likely to differ in their ability to either withstand or recover from oil. And this variation in marsh response provides a prime opportunity for us to learn more about the specific marsh characteristics that either hinder or promote recovery, information that could be valuable in the aftermath of this disaster.

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"marsh 2," location of the species diversity experiment

One aspect of marshes that may aid in the response to oil is plant species diversity. A substantial number of scientific studies in the ocean and on land illustrate that having more species in an area can reduce the impacts of disturbance. For example, research by David Tilman and colleagues shows that drought impacts are less severe in Minnesota grasslands with more plant species. A number of different processes can contribute to these positive effects of diversity, but they generally result from the fact that individual species typically differ in their life history (the timing of growth, reproduction, etc.) and in their response to specific disturbances. Thus, if you have more species, you’re more likely to contain one or two that are able to withstand disturbance as it occurs, or that are able to re-grow quickly following the disturbance.

So, back to salt marshes and oil. We know from previous studies that different marsh plants have different tolerances for oil (1,2). Because the chances of a more tolerant plant species being present are greater when there are more plant species around, it seems possible that marsh plant diversity could reduce the negative impacts of oil exposure. We’ll get some idea of whether or not this is the case from our surveys of natural marshes – we know the plant species diversity before oil gets there, and we’ll be able to record the impacts to the marsh once oil arrives to see if the negative effects are reduced in areas with more species. But to get the “real” story (i.e., a story not complicated by characteristics other than plant species diversity that vary from marsh to marsh), we need to do an experiment.

Recently, we did just that – we set up an experiment to test whether marshes (“plots”) with more species (3) are less impacted by oil than marshes with few species (1). 3 species may not seem particularly diverse, but it’s on par with what we find in natural marshes. There’s a chance that our experimental site won’t get any oil, which quite honestly will be fine by me. (In that case, we’ll simply look at how marsh productivity and growth differ due to marsh plant species diversity.) But, if it does, we’ll be positioned to examine how marsh plant species diversity affects the response to oil contamination.

Randall’s research is funded by the National Science Foundation.

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What were we doing before Deepwater Horizon?

Dr. Randall Hughes FSU Coastal & Marine Lab

Watch the “snail experiment.”
Snails in the marsh

Periwinkle snails climbing on cordgrass

IGOR chip- biodiversity 150One of the marsh animals that we have been studying for the last year (in the absence of oil) is the marsh periwinkle, Littoraria irrorata. This snail is very abundant in many marshes and is particularly visible at high tide when it climbs the plant stems to get out of the water and away from its predators, primarily crown conchs and blue crabs.

While hanging out on the cordgrass stems, the snails will often create grazing scars that look much like a razor blade cut through the grass. Even though they don’t remove much plant tissue, they can have a big impact – fungus colonizes their grazing scars, and if the fungus becomes abundant enough, it can kill the entire plant, leading to marsh loss. (See the excellent work done by Brian Silliman at UF on this topic.)

One of the interesting aspects of many Panhandle marshes is that needlerush, a taller plant than cordgrass that usually occurs closer to land, can grow side-by-side with cordgrass at the water’s edge.

When needlerush is there, lots of snails climb on it despite the fact that they don’t eat it. (We think they like needlerush because it is taller and provides a better escape from predators than cordgrass.)

Because we noticed that the cordgrass that occurs with needlerush is taller and healthier than cordgrass that occurs in patches by itself, we are currently conducting an experiment to see if this pattern is due to the snails spending less time on cordgrass when needlerush is around. Each experimental plot is surrounded by a cage that serves to keep snails either in or out so that we can test their effects on the plants. You may notice the snails are very fashionable – we ‘tag’ them with nail polish so that we can differentiate the ones we put in the cages from ones that get in from the surrounding marsh. Some cages contain cordgrass only, whereas others contain a mix of needlerush and cordgrass. Finally, in some of the cages we have clipped the above-ground portions of all of the neighboring plants – this allows us to see whether the cordgrass simply prefers the environment that needlerush grows in, or if the needlerush must be present for the cordgrass to benefit.

As long as our experiment isn’t prematurely interrupted by oil, then we should have an answer to our question by the end of the summer!

Randall’s research is funded by the National Science Foundation. The song used in the video is Florida Breeze, by Craig Reeder.

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What we are doing “In the Grass”

Dr. Randall Hughes FSU Coastal & Marine Lab

IGOR chip- biodiversity 150As a marine ecologist at the Florida State University Coastal and Marine Laboratory, my everyday job is to try to understand the plant and animal communities along our coast and then communicate that knowledge to students, other scientists, and the public.  Much of my research focuses on understanding how the biodiversity, or the number of species or genetic individuals, of coastal communities such as salt marshes influences their productivity and ability to respond to disturbances.  Don’t let the terminology scare you – the basic idea is similar to having a diversified stock portfolio: by having a greater variety of species or ‘genotypes,’ aka more diversity, you increase the chances that one of them will grow really well, attract lots of critters, survive a disaster, etc.  Think of it as the spare tire theory of ecology!

I work with undergraduate and graduate students, research assistants, and volunteers to study the marshes and seagrass beds of the FL Panhandle and Big Bend regions.

IMG_0038Because large portions of the Gulf of Mexico are currently threatened by the Deepwater Horizon oil spill, this work suddenly has an increased urgency for me, personally, as well as for many other citizens who are concerned about what this oil may do to the waters, coasts, plants, and animals that we love.  In this blog, I’ll give you an overview of what we’re doing in regards to the oil spill, as well as on a daily basis in the absence of major disasters, to highlight the ups and downs and funny moments associated with being a scientist.

As awareness of the magnitude of the Deepwater Horizon oil spill has increased, my lab and I have focused our efforts on documenting the current state of salt marshes in our area.  This work includes identifying and counting the dominant plant species in the marsh, as well as the many marine critters (crabs or snails, such as the marsh periwinkle, below) and bugs (spiders, grasshoppers, and other insects) that live here.  Bug collecting is perhaps the most attention-grabbing (as you’ll see in the video below), involving the use of a gas-powered vacuum to suck the insects into mesh bags so that we can then preserve and identify them in the lab.

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Because plant genetic diversity can be very important for the ability of these plants to respond to disturbance, we’re also collecting small pieces of plant tissue that can be analyzed in the lab using DNA markers to determine how many different genetic individuals are present.  Finally, we’re collecting samples of dirt to document the amount of hydrocarbons (a signature of oil exposure) in the marsh sediment.  Although we still fervently hope that none of the oil reaches these marshes, such “pre-spill” data will allow us to document as completely as possible the impacts of this spill on our coast, inform the recovery of these areas, and work to prevent similar incidents in the future.

Special thanks to Bill Wharton, who provided music for the video piece.
Randall’s research is funded by the National Science Foundation.
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